Prostatic stent

Abstract: A prostatic stent having an elongate body (13) defining a passage therethrough and comprising a distal section (17), a mid-section (19) and a proximal section (21), said elongate body (13) having a length sufficient to extend distally from a bladder neck (3) to a position somewhat short of the external sphincter (9), and said proximal section (21) having a shape conforming to the neck (3) of the urinary bladder (1); and processes for the manufacture of such prostatic stent of a metallic braided type.

Description: Technical field The present invention relates to a prostatic stent comprising an elongate body which defines a passage therethrough, and the invention also covers processes for the manufacture of such prostatic stent made of a metallic material. Such stents corresponding to the preamble of claim 1 are known c.f. from EP-A-0481365 or EP-A-0183372. Thus, the invention more specifically relates to a prostatic stent for non-surgical treatment of obstruction of prostatic urethra, such as may arise in connection with benign prostatic hyperplasia or prostatic carcinoma. Background of the invention A commonly occurring disorder in urology is the obstruction of prostatic urethra. The disorder occurs in males due to enlargement of the prostatic gland, due to either hyperplasia or cancer. A condition often found in older males is known as benign prostatic hyperplasia (BPH), and said condition can cause a plurality of inconvenient symptoms, such as difficulties to urinate, strongly reduced capacity to urinate, and the condition may at times result in complete retention of urine which may lead to severe renal disorders. The traditional procedure for treating problems associated with enlargement of the prostate gland has up to now been surgery constituted by cutting away interior sections of the prostate gland or complete surgical removal of the prostate. These are, however, procedures unfavoured by many patients and there has been a search for alternative ways of dealing with the problem. US patent 5,059,169 is an example of such alternative to surgery. Said patent discloses a prostatic stent provided with a conical flange disposed within the neck of the bladder, the opposite end of the stent body extending approximately to the verumontanum. The stent is provided with a textured exterior surface that frictionally engages the urethral walls to prevent migration of the stent into the bladder. Migration in the opposite direction is prevented by the conical flange. However, this prior art high-friction prostatic stent is associated with disadvantages, in particular at and around the conical flange disposed within the neck of the bladder due to the fact that said end of the stent does not conform to the bladder neck in view of the fact that the proximal end of the stent is designed perpendicular to a center line of the body of the stent. This design means that the stent cannot be placed optimally to cover the complete bladder neck. Either it causes urinary stones (calculi, encrustation) to form on the device protruding into the bladder or the device does not completely cover the circumference of the bladder neck when the stent is placed further down the prostatic urethra running the risk of not relieving the obstruction. Other examples of prior art are the disclosures of EP-A-0481 365 and WO91/16005. These documents disclose devices for implantation to keep corporeal conduits open, such as widening stenosis in body vessels. The devices have not been designed specifically for prostatic implantation and thus do not conform to a corresponding shape. Other examples of prior art devices intended for prostatic implantation are disclosed in EP-A-0 183 372 and US-A-4,994,066. Although intended for prostatic use these devices are, again, not designed to conform to the implantation site and do therefore not perform in a desirable way. Summary of the invention One object of the present invention is to provide an improved prostatic stent for the treatment of bladder outlet obstruction caused by an enlarged prostate. Another object of the present invention is to provide a prostatic stent having a shape conformed to the neck of the urinary bladder to avoid urinary calculi or encrustation or to avoid uncovered areas of the prostatic urethra adjacent to the bladder neck. Still another object of the invention is to provide a prostatic stent while avoiding migration of the stent into the bladder or distally towards the sphincter. Yet another object of the invention is to provide processes for the manufacture of metallic braided prostatic stents showing improved performance when used for solving the problem of non-surgical management of bladder outlet obstruction. Other objects and advantages of the present invention will be understood upon reading of the following disclosure taken together with the drawing and the appended claims. Thus, the invention resides in a prostatic stent having an elongate body defining a passage therethrough and comprising a distal section, a mid-section and a proximal section, said mid-section having a substantially constant cross-section along said mid-section, characterized in that said proximal section has a flaring and oblique proximal end conforming both radially and axially to the walls of the surrounding bladder neck, and that said elongate body has a length sufficient to extend distally from a bladder neck to a position somewhat short of the external sphincter, such as up to and/or passing the verumontanum, In order to conform to the neck of the urinary bladder it is preferred that the proximal end of said proximal section extends in a plane sloping at an angle to a normal to a center line of the body not exceeding about 50ø. It is particularly preferred that said angle lies within the range of about 5 to about 40°, such as within a range of about 10 to about 30°. In a preferred embodiment of the invention said mid-section has a substantially constant cross-section along said mid-section, i.e. said cross-section has a crosssectional area and shape that are substantially constant along said section. As indicated above the prostatic stent of the invention extends to the bladder neck up to a position at least short of the verumontanum and it can extend all the way up to short of the sphincter. It is, of course, important that the stent extends short of the sphincter so as not to interfere with the normal function of the sphincter. In embodiments where the stent extends to a position short of the sphincter and adjacent to the verumontanum it is preferred that the body has a distally directed flare to prevent proximal migration of the stent thereby conforming to the surrounding urethral wall. On the other hand, in embodiments where the stent extends beyond the verumontanum and up to a position short of the sphincter, it is preferred that the body has a distally directed taper so as not to interfere with the sphincter function. In the instant disclosure the term "distal" or "distally" refers to a direction from the inside of the patient body to the exterior thereof, whereas the term "proximal" or "proximally" refers to the opposite direction. The prostatic stent according to the invention may have an approximately circular radial cross-section, or it may have a non-circular radial cross-section for improved conformation to the surrounding urethral wall. In the latter case said non-circular radial cross-section may be of a flattened or oval shape. It is preferred that the prostatic stent according to the invention is of a self-expandable type. An example of particularly preferred self-expandable stent is found in US patent 4,655,771. Such stent is thus of the braided type comprising a flexible tubular body which has a diameter that is variable by axial movement of the ends of the body relative to each other and which is composed of several individual rigid but flexible thread elements each of which extends in helix configuration with the center line of the body as a common axis, a number of elements having the same direction of winding but being axially displaced relative to each other crossing a number of elements also axially displaced relative to each other but having the opposite direction of winding. In a particularly preferred embodiment of such prostatic stent the proximal end of the body extends in the plane that is substantially parallel to the oppositely extending filaments in the stent. The invention also resides in a process for the manufacture of a metallic braided prostatic stent as disclosed above, said process comprising preparing a braided hollow, deformable body having substantially straight cylindrical walls, characterized by the steps: a) mounting the deformable body onto a mandrel with a shape corresponding to the above described particular desired shape of the finished stent; b) applying energy or external pressure or both onto said body positioned on said mandrel to cause said body to conform to the shape of the mandrel; c) removing the thus shaped body from the mandrel; and d) cutting the proximal end to the desired obliqueness. In an alternative process of the invention for the manufacture of the metallic braided prostatic stent the steps involved are the following: a) providing a braiding bar with a shape corresponding to the above described particular shape of the finished stent; b) preparing a braided body by performing the braiding of the filaments on said braiding bar; c) removing said braided body from said braiding bar, optionally after the application of energy and/or pressure of said body while placed on said bar; and d) cutting the proximal end to the desired obliqueness. In yet an alternative process of the invention for the manufacture of a metallic braided prostatic stent, the process comprises the steps: a) providing a braiding bar, the radial cross-section of which is substantially constant along its entire length; b) preparing a braided body by performing the braiding at varying axial speed of said braiding bar to obtain a varying angle between the crossing filaments along said bar; and c) mounting the body resulting from step b) onto a mandrel with a shape corresponding to the above described particular desired shape of the finished stent; and d) applying energy and/or pressure to said body when placed on said mandrel to cause said body to conform to the shape of the mandrel and removing the thus shaped body from the mandrel; and e) cutting the proximal end to the desired obliqueness. Brief description of the drawing The enclosed drawing is a perspective view in cross-section in a sagittal plane showing the urinary tract and bladder and the prostatic stent according to the invention in an implanted position within the urethral tract. Detailed description of the disclosed embodiment With reference to the drawing there is shown in a diagramatic manner a cross-section in a sagittal plane of the area surrounding the urinary tract including the bladder. In the drawing, there is shown the bladder 1 having a tapered neck 3. The bladder neck 3 tapers into the urethra 5, and the prostatic part 11 of the urethra 5, approximately 3 to 4 cm thereof, is surrounded by the prostate gland 7. In the drawing there is also diagramatically shown the external sphincter 9, whose normal function is to keep the urethra closed until urination when it opens for emptying the bladder 1. On the rear wall of the urethra 5 (more particularly the upper portion 11 thereof) there is a small projection, the verumontanum 10. Shown in an implanted position in the upper part of urethra 5 a stent 13 in accordance with the invention is placed. Said sections 17,19,21 form an elongate body 13 constituting the stent proper. A center line L through said elongate body 13 is shown in the drawing. The embodiment of the stent 13 shown in the drawing is designed in accordance with the prosthesis for transluminal implantation disclosed in US patent 4,655,771. For details regarding this type of stent reference is made to the disclosure of said US patent. It is preferred that the stent is made of a material possessing springiness or agility combined with suitable elasticity. A preferred material is a medicinally acceptable metal, for example Phynox® , Elgiloy® , MP35N® or titanium. The proximal end 23 of stent 13 is designed to conform to the neck 3 of the urinary bladder 1. As shown in the drawing the plane P of the proximal end 23 of stent 13 has a sloping extension under an angle α to the normal N to the center line L of the elongate stent body. This sloping extension of proximal end 23 results in a stent configuration closely conforming to the surrounding neck 3 of bladder 1 resulting in advantages to be explained below. In the embodiment shown in the drawing the distal section 17 of stent 13 extends up to a position short of sphincter 9 and has a distally directed taper so as not to interfere with the sphincter function. Said distal section 17 of the stent may also extend to a position somewhat short of the verumontanum 10 and is then preferably provided with a distally directed flare for the purpose of preventing proximal migration of the stent and also to conform to the surrounding urethral wall. The procedure for preparing for implantation and the implantation proper will now be described in some detail. In order to select the correct size of the prostatic stent the urologist determines the length of the prostatic urethra. The length of the prostatic urethra from the bladder neck to the verumontanum or to the sphincter, respectively, can be determined by using a measuring catheter. The measures taken up to this point are largely conventional to the skilled urologist. After selection of the appropriate stent size due consideration being taken of the fact that the stent must be shorter than the measured length of the prostatic urethra to allow for the natural elongation of the stent in response to the pressure of the enclosing urethral walls, the prostatic stent applied to a suitable delivery instrument is then inserted into the prostatic urethra via penis and the urethral tract to the position shown in the drawing. It is important to note that the sloping end 23 of the stent 13 has the orientation shown in the drawing, i.e. the slope being directed to be at a maximum in the direction of the sagittal plane through the center line L of the stent body 13. It is important to note that the prostatic stent does not extend into the external sphincter because such position of the stent will cause incontinence to the patient. After proper positioning of the stent the stent is released from the implantation instrument, and the instrument is withdrawn and removed from the patient. The feature of the proximal section 21 of the stent 13 being designed with a shape conforming to the neck 3 of the urinary bladder 1 results in important advantages in practical use of the stent. Thus, as is understood from the drawing, the conformed shape of the proximal end 23 of the proximal section 21 of stent 13 means that urinary calculi or encrustation cannot accumulate on the stent due to the fact that it fits snugly to the interior of the neck 3 of bladder 1 and becomes covered with tissues after implantation. Nor will there be uncovered parts on the other side of the stent. The stent will perform its opening and supporting functions all the way to the entire bladder neck without allowing wires to protrude into the bladder which could become calcified. Furthermore, the proximal flare of the proximal section 21 of the stent prevents the stent from distal migration towards the sphincter 9. On the other hand, in embodiments where the distal section 17 of the stent has a distally directed flare proximal migration of the stent into the bladder will be prevented.

Claims: A prostatic stent having an elongate body (13) defining a passage therethrough, and comprising a proximal section (21), a mid-section (19) having a substantially constant cross-section along said mid-section, and a distal section (17) characterized in that said proximal section (21) has a flaring and oblique proximal end (23) conforming both radially and axially to the walls of the surrounding bladder neck (3), and that said elongate body (13) has a length sufficient to extend distally from a bladder neck (3) to a position somewhat short of the external sphincter (9). A prostatic stent according to claim 1, wherein the proximal end (23) of said proximal section (21) extends in a plane (P) sloping at an angle (α) to a normal (N) to a center line (L) of said body (13) not exceeding about 50°. A prostatic stent according to claim 2, wherein said angle (α) lies within a range of about 5 to about 40°. A prostatic stent according to claim 3, wherein said angle (α) lies within a range of about 10 to about 30°. A prostatic stent according to any preceding claim, wherein said distal section (17) of the body (13) has a distally directed taper so as not to interfere with the sphincter function. A prostatic stent according to any preceding claim, wherein said body (13) has an approximately circular radial cross-section. A prostatic stent according to any of claims 1 to 5, wherein said body (13) has a non-circular radial cross-section for improved conformation to the surrounding urethral wall. A prostatic stent according to claim 10, wherein said non-circular radial cross-section has a flattened or oval shape. A prostatic stent according to any preceding claim, which is of a self-expandable type. A prostatic stent according to claim 9, which is of the braided type comprising a flexible tubular body which has a diameter that is variable by axial novement of the ends of the body relative to each other and which is composed of several individual rigid but flexible thread elements each of which extends in helix configuration with the center line of the body as a common axis, a number of elements having the same direction of winding but being axially displaced relative to each other crossing a number of elements also axially displaced relative to each other but having the opposite direction of winding. A prostatic stent according to claim 10, wherein said proximal end (23) of said body (13) extends in a plane that is substantially parallel to the oppositely extending filaments in the stent. A process for the manufacture of a metallic braided prostatic stent having an elongate body (13) defining a passage therethrough, and comprising a proximal section (21) having a flaring and oblique proximal end (23) conforming both radially and axially to the walls of the surrounding bladder neck (3), further comprising a mid-section (19) having a substantially constant cross-section along said mid-section, and a distal section (17), said process comprising preparing a braided hollow, deformable body having substantially straight cylindrical walls, characterized by a) mounting the deformable body onto a mandrel with a shape corresponding to the above defined particular desired shape of the finished stent; b) applying energy or external pressure or both onto said body positioned on said mandrel to cause said body to conform to the shape of the mandrel; c) removing the thus shaped body from the mandrel; and d) cutting the proximal end (23) to the desired obliqueness. A process for the manufacture of a metallic braided prostatic stent having an elongate body (13) defining a passage therethrough, and comprising a proximal section(21) having a flaring and oblique proximal end (23) conforming both radially and axially to the walls of the surrounding bladder neck (3), further comprising a mid-section (19) having a substantially constant diameter, and a distal section (17), said process comprising the steps: a) providing a braiding bar with a shape corresponding to the above described particular shape of the finished stent; b) preparing a braided body by performing the braiding of the filaments on said braiding bar; c) removing said braided body from said braiding bar, optionally after the application of energy and/or pressure of said body while placed on said bar; and d) cutting the proximal end (23) to the desired obliqueness. A process for the manufacture of a metallic braided prostatic stent having an elongate body (13) defining a passage therethrough, and comprising a proximal section (21) having a flaring and oblique proximal end (23) conforming both radially and axially to the walls of the surrounding bladder neck (3), further comprising a mid-section (19) having a substantially constant diameter, and a distal section (17), said process comprising the steps: a) providing a braiding bar, the radial cross-section of which is substantially constant along its enti re length; b) preparing a braided body by performing the braiding at varying axial speed of said braiding bar to obtain a varying angle between the crossing filaments along said bar; c) mounting the body resulting from step b) onto a mandrel with a shape corresponding to the above described particular desired shape of the finished stent; d) applying energy and/or pressure to said body when placed on said mandrel to cause said body to conform to the shape of the mandrel and removing the thus shaped body from the mandrel; and e) cutting the proximal end (23) to the desired obliqueness.

Inventors: BURTON JOHN, CLERC CLAUDE, FURRER ADRIAN, JEDWAB MICHAEL, MARILLER ALAIN, MIKULICH MICHAEL, TIHON CLAUDE, BURTON, JOHN, CLERC, CLAUDE, FURRER, ADRIAN, JEDWAB, MICHAEL, MARILLER, ALAIN, MIKULICH, MICHAEL, TIHON, CLAUDE
Applicants: MEDINVENT AMS SA, AMS MEDINVENT S.A.
Application year: 1994
Main classification: A61F2
IPC codes: A61F2